EVENT Category

The EVENT category contains the node tree entry points and engine event detectors. These are the nodes that start execution or trigger it in response to something that happens in the scene.

Three groups

Entry Points

Nodes with no In socket. They are the root of the tree — the compiler generates a separate Python method for each one.

Node	When it executes
On Start	Once when the component is created
On Update	Every frame

Event detectors

Nodes with an In socket that branch execution based on whether an event occurred:

Node	Type	Detected event
On Key Press	Branch (True/False)	Key pressed / held / released
On Collision	Branch (Hit/None)	Collision with another object
On Mouse Move	Branch (Moving/Still)	Cursor movement
On Timer	Branch (Elapsed/Waiting)	Internal countdown
On Property Change	Branch (Changed/Same)	BGE property value change

Message bus

A pair of nodes for communication between objects without direct references:

Node	Role
On Message	Receiver — waits for a message with a subject
Node Broadcast	Sender — sends the message to all receivers

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When to use each

One-time startup           → On Start
Every frame                → On Update
Keyboard input             → On Key Press
Physical collision         → On Collision
Mouse movement             → On Mouse Move
Internal periodic event    → On Timer
React to BGE property      → On Property Change
Cross-object communication → On Message + Node Broadcast

Multiple entry points in the same tree

A tree can have both On Start and On Update (and multiple of each). The compiler generates a separate method for each:

def start(self):
    # → nodes connected to On Start

def update(self):
    # → nodes connected to On Update

All other nodes (detectors, FLOW, AI…) must be connected to one of these entry points to execute.

On Timer vs Delay (FLOW)

On Timer	Delay (FLOW)
Own entry point	Requires OnUpdate as root
Countdown with deltaTime()	Absolute clock getClockTime()
Exposes Progress socket (0→1)	No progress
Repeat = True by default	Repeat = False by default

On Message vs native sendMessage()

Node Broadcast + On Message use globalDict — they work between RNC Python components. Range's native sendMessage() uses the Logic Bricks system and is not compatible with this bus.